1. Field of the Invention
The present invention relates to an ophthalmic apparatus for examining or measuring an eye to be examined.
2. Description of Related Art
With an ophthalmic apparatus for obtaining data about characteristics of an eye to be examined, such as eye refractive power or corneal shape, an examinee""s head is stably fixed on a head rest or the like. Thereafter, a measurement part (a measurement optical system) is aligned with the eye and then measurement is performed.
Recently, in order to save trouble of an examiner to make fine alignment, there has been suggested an apparatus having an auto-alignment mechanism which detects an alignment condition of the measurement part with respect to the eye and automatically moves the measurement part based on the thus detected result.
With this kind of apparatus, however, it is often the case where an examinee""s head is inclined with respect to a horizontal reference although the examinee""s head is fixed by using a head rest or the like. There is also possibility that the examinee""s head may move at the time of shifting the measurement part from one eye to the other after completion of measurement on the first eye. Measurement performed under such a condition is likely to end up in inaccurate measurement results, namely astigmatic axial (cylindrical axial) angles, refractive power in the principal meridian direction, or the like. Especially in the case where refractive power data or corneal shape data is used in keratorefractive surgery for correcting refractive error by ablating the cornea using an excimer laser beam, the astigmatic axial angle data is desired to be highly accurate.
Further, with this kind of apparatus having an auto-alignment mechanism, the measurement part automatically tracks movement of the eye and the measurement is performed automatically upon completion of the alignment. Therefore, it is difficult to grasp the movement of the eye. If the eye is not stably fixed, measurement results obtained thereby will be of poor reliability.
The present invention has been made in view of the above circumstances and has an object to overcome the above problems and to provide an ophthalmic apparatus with which highly reliable measurement results are obtained.
Additional objects and advantages of the invention will be set forth in part in the description which follows and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the objects and in accordance with the purpose of the present invention, as embodied and broadly described herein, an ophthalmic apparatus for measuring a characteristic of an eye to be examined, the apparatus comprises moving means for relatively moving a measurement unit with respect to the eye, wherein the measurement unit includes a measurement system for measuring the characteristic of the eye, position detecting means for detecting a relative position of the measurement unit with respect to the eye at the time of measurement, storing means for storing detected position data, and processing means for performing a predetermined processing based on a plurality of position data stored in each measurement.